package com.zh.security.queue;

import java.util.concurrent.BlockingQueue;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;
import java.util.AbstractQueue;
import java.util.Collection;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Spliterator;
import java.util.Spliterators;
import java.util.function.Consumer;

/**
 * An optionally-bounded {@linkplain BlockingQueue blocking queue} based on
 * linked nodes.
 * This queue orders elements FIFO (first-in-first-out).
 * The <em>head</em> of the queue is that element that has been on the
 * queue the longest time.
 * The <em>tail</em> of the queue is that element that has been on the
 * queue the shortest time. New elements
 * are inserted at the tail of the queue, and the queue retrieval
 * operations obtain elements at the head of the queue.
 * Linked queues typically have higher throughput than array-based queues but
 * less predictable performance in most concurrent applications.
 *
 * <p>The optional capacity bound constructor argument serves as a
 * way to prevent excessive queue expansion. The capacity, if unspecified,
 * is equal to {@link Integer#MAX_VALUE}.  Linked nodes are
 * dynamically created upon each insertion unless this would bring the
 * queue above capacity.
 *
 * <p>This class and its iterator implement all of the
 * <em>optional</em> methods of the {@link Collection} and {@link
 * Iterator} interfaces.
 *
 * <p>This class is a member of the
 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
 * Java Collections Framework</a>.
 *
 * @since 1.5
 * @author Doug Lea
 * @param <E> the type of elements held in this collection
 */
public class MyLinkedBlockingQueue<E> extends AbstractQueue<E>
		implements BlockingQueue<E>, java.io.Serializable {
//	private static final long serialVersionUID = -6903933977591709192L;

	/*
	 * A variant of the "two lock queue" algorithm.  The putLock gates
	 * entry to put (and offer), and has an associated condition for
	 * waiting puts.  Similarly for the takeLock.  The "count" field
	 * that they both rely on is maintained as an atomic to avoid
	 * needing to get both locks in most cases. Also, to minimize need
	 * for puts to get takeLock and vice-versa, cascading notifies are
	 * used. When a put notices that it has enabled at least one take,
	 * it signals taker. That taker in turn signals others if more
	 * items have been entered since the signal. And symmetrically for
	 * takes signalling puts. Operations such as remove(Object) and
	 * iterators acquire both locks.
	 *
	 * Visibility between writers and readers is provided as follows:
	 *
	 * Whenever an element is enqueued, the putLock is acquired and
	 * count updated.  A subsequent reader guarantees visibility to the
	 * enqueued Node by either acquiring the putLock (via fullyLock)
	 * or by acquiring the takeLock, and then reading n = count.get();
	 * this gives visibility to the first n items.
	 *
	 * To implement weakly consistent iterators, it appears we need to
	 * keep all Nodes GC-reachable from a predecessor dequeued Node.
	 * That would cause two problems:
	 * - allow a rogue Iterator to cause unbounded memory retention
	 * - cause cross-generational linking of old Nodes to new Nodes if
	 *   a Node was tenured while live, which generational GCs have a
	 *   hard time dealing with, causing repeated major collections.
	 * However, only non-deleted Nodes need to be reachable from
	 * dequeued Nodes, and reachability does not necessarily have to
	 * be of the kind understood by the GC.  We use the trick of
	 * linking a Node that has just been dequeued to itself.  Such a
	 * self-link implicitly means to advance to head.next.
	 */

	/**
	 * Linked list node class
	 */
	static class Node<E> {
		E item;

		/**
		 * One of:
		 * - the real successor Node
		 * - this Node, meaning the successor is head.next
		 * - null, meaning there is no successor (this is the last node)
		 */
		Node<E> next;

		Node(E x) { item = x; }
	}

	/** The capacity bound, or Integer.MAX_VALUE if none */
	private final int capacity;

	/** Current number of elements */
	private final AtomicInteger count = new AtomicInteger();

	/**
	 * Head of linked list.
	 * Invariant: head.item == null
	 */
	transient Node<E> head;

	/**
	 * Tail of linked list.
	 * Invariant: last.next == null
	 */
	private transient Node<E> last;

	/** Lock held by take, poll, etc */
	private final ReentrantLock takeLock = new ReentrantLock();

	/** Wait queue for waiting takes */
	private final Condition notEmpty = takeLock.newCondition();

	/** Lock held by put, offer, etc */
	private final ReentrantLock putLock = new ReentrantLock();

	/** Wait queue for waiting puts */
	private final Condition notFull = putLock.newCondition();

	/**
	 * Signals a waiting take. Called only from put/offer (which do not
	 * otherwise ordinarily lock takeLock.)
	 */
	private void signalNotEmpty() {
		final ReentrantLock takeLock = this.takeLock;
		takeLock.lock();
		try {
			notEmpty.signal();
		} finally {
			takeLock.unlock();
		}
	}

	/**
	 * Signals a waiting put. Called only from take/poll.
	 */
	private void signalNotFull() {
		final ReentrantLock putLock = this.putLock;
		putLock.lock();
		try {
			notFull.signal();
		} finally {
			putLock.unlock();
		}
	}

	/**
	 * Links node at end of queue.
	 *
	 * @param node the node
	 */
	private void enqueue(Node<E> node) {
		// assert putLock.isHeldByCurrentThread();
		// assert last.next == null;
		last = last.next = node;
	}

	/**
	 * Removes a node from head of queue.
	 *
	 * @return the node
	 */
	private E dequeue() {
		// assert takeLock.isHeldByCurrentThread();
		// assert head.item == null;
		Node<E> h = head;
		Node<E> first = h.next;
		h.next = h; // help GC
		head = first;
		E x = first.item;
		first.item = null;
		return x;
	}

	/**
	 * Locks to prevent both puts and takes.
	 */
	void fullyLock() {
		putLock.lock();
		takeLock.lock();
	}

	/**
	 * Unlocks to allow both puts and takes.
	 */
	void fullyUnlock() {
		takeLock.unlock();
		putLock.unlock();
	}

//     /**
//      * Tells whether both locks are held by current thread.
//      */
//     boolean isFullyLocked() {
//         return (putLock.isHeldByCurrentThread() &&
//                 takeLock.isHeldByCurrentThread());
//     }

	/**
	 * Creates a {@code LinkedBlockingQueue} with a capacity of
	 * {@link Integer#MAX_VALUE}.
	 */
	public MyLinkedBlockingQueue() {
		this(Integer.MAX_VALUE);
	}

	/**
	 * Creates a {@code LinkedBlockingQueue} with the given (fixed) capacity.
	 *
	 * @param capacity the capacity of this queue
	 * @throws IllegalArgumentException if {@code capacity} is not greater
	 *         than zero
	 */
	public MyLinkedBlockingQueue(int capacity) {
		if (capacity <= 0) throw new IllegalArgumentException();
		this.capacity = capacity;
		last = head = new Node<E>(null);
	}

	/**
	 * Creates a {@code LinkedBlockingQueue} with a capacity of
	 * {@link Integer#MAX_VALUE}, initially containing the elements of the
	 * given collection,
	 * added in traversal order of the collection's iterator.
	 *
	 * @param c the collection of elements to initially contain
	 * @throws NullPointerException if the specified collection or any
	 *         of its elements are null
	 */
	public MyLinkedBlockingQueue(Collection<? extends E> c) {
		this(Integer.MAX_VALUE);
		final ReentrantLock putLock = this.putLock;
		putLock.lock(); // Never contended, but necessary for visibility
		try {
			int n = 0;
			for (E e : c) {
				if (e == null)
					throw new NullPointerException();
				if (n == capacity)
					throw new IllegalStateException("Queue full");
				enqueue(new Node<E>(e));
				++n;
			}
			count.set(n);
		} finally {
			putLock.unlock();
		}
	}

	// this doc comment is overridden to remove the reference to collections
	// greater in size than Integer.MAX_VALUE
	/**
	 * Returns the number of elements in this queue.
	 *
	 * @return the number of elements in this queue
	 */
	@Override
	public int size() {
		return count.get();
	}

	// this doc comment is a modified copy of the inherited doc comment,
	// without the reference to unlimited queues.
	/**
	 * Returns the number of additional elements that this queue can ideally
	 * (in the absence of memory or resource constraints) accept without
	 * blocking. This is always equal to the initial capacity of this queue
	 * less the current {@code size} of this queue.
	 *
	 * <p>Note that you <em>cannot</em> always tell if an attempt to insert
	 * an element will succeed by inspecting {@code remainingCapacity}
	 * because it may be the case that another thread is about to
	 * insert or remove an element.
	 */
	public int remainingCapacity() {
		return capacity - count.get();
	}

	/**
	 * Inserts the specified element at the tail of this queue, waiting if
	 * necessary for space to become available.
	 *
	 * @throws InterruptedException {@inheritDoc}
	 * @throws NullPointerException {@inheritDoc}
	 */
	public void put(E e) throws InterruptedException {
		if (e == null) throw new NullPointerException();
		// Note: convention in all put/take/etc is to preset local var
		// holding count negative to indicate failure unless set.
		int c = -1;
		Node<E> node = new Node<E>(e);
		final ReentrantLock putLock = this.putLock;
		final AtomicInteger count = this.count;
		putLock.lockInterruptibly();
		try {
			/*
			 * Note that count is used in wait guard even though it is
			 * not protected by lock. This works because count can
			 * only decrease at this point (all other puts are shut
			 * out by lock), and we (or some other waiting put) are
			 * signalled if it ever changes from capacity. Similarly
			 * for all other uses of count in other wait guards.
			 */
			while (count.get() == capacity) {
				notFull.await();
			}
			enqueue(node);
			c = count.getAndIncrement();
			if (c + 1 < capacity)
				notFull.signal();
		} finally {
			putLock.unlock();
		}
		if (c == 0)
			signalNotEmpty();
	}

	/**
	 * Inserts the specified element at the tail of this queue, waiting if
	 * necessary up to the specified wait time for space to become available.
	 *
	 * @return {@code true} if successful, or {@code false} if
	 *         the specified waiting time elapses before space is available
	 * @throws InterruptedException {@inheritDoc}
	 * @throws NullPointerException {@inheritDoc}
	 */
	public boolean offer(E e, long timeout, TimeUnit unit)
			throws InterruptedException {

		if (e == null) throw new NullPointerException();
		long nanos = unit.toNanos(timeout);
		int c = -1;
		final ReentrantLock putLock = this.putLock;
		final AtomicInteger count = this.count;
		putLock.lockInterruptibly();
		try {
			while (count.get() == capacity) {
				if (nanos <= 0)
					return false;
				nanos = notFull.awaitNanos(nanos);
			}
			enqueue(new Node<E>(e));
			c = count.getAndIncrement();
			if (c + 1 < capacity)
				notFull.signal();
		} finally {
			putLock.unlock();
		}
		if (c == 0)
			signalNotEmpty();
		return true;
	}

	/**
	 * Inserts the specified element at the tail of this queue if it is
	 * possible to do so immediately without exceeding the queue's capacity,
	 * returning {@code true} upon success and {@code false} if this queue
	 * is full.
	 * When using a capacity-restricted queue, this method is generally
	 * preferable to method {@link BlockingQueue#add add}, which can fail to
	 * insert an element only by throwing an exception.
	 *
	 * @throws NullPointerException if the specified element is null
	 */
	public boolean offer(E e) {
		if (e == null) throw new NullPointerException();
		final AtomicInteger count = this.count;
		if (count.get() == capacity)
			return false;
		int c = -1;
		Node<E> node = new Node<E>(e);
		final ReentrantLock putLock = this.putLock;
		putLock.lock();
		try {
			if (count.get() < capacity) {
				enqueue(node);
				c = count.getAndIncrement();
				if (c + 1 < capacity)
					notFull.signal();
			}
		} finally {
			putLock.unlock();
		}
		if (c == 0)
			signalNotEmpty();
		return c >= 0;
	}

	public E take() throws InterruptedException {
		E x;
		int c = -1;
		final AtomicInteger count = this.count;
		final ReentrantLock takeLock = this.takeLock;
		takeLock.lockInterruptibly();
		try {
			while (count.get() == 0) {
				notEmpty.await();
			}
			x = dequeue();
			c = count.getAndDecrement();
			if (c > 1)
				notEmpty.signal();
		} finally {
			takeLock.unlock();
		}
		if (c == capacity)
			signalNotFull();
		return x;
	}

	public E poll(long timeout, TimeUnit unit) throws InterruptedException {
		E x = null;
		int c = -1;
		long nanos = unit.toNanos(timeout);
		final AtomicInteger count = this.count;
		final ReentrantLock takeLock = this.takeLock;
		takeLock.lockInterruptibly();
		try {
			while (count.get() == 0) {
				if (nanos <= 0)
					return null;
				nanos = notEmpty.awaitNanos(nanos);
			}
			x = dequeue();
			c = count.getAndDecrement();
			if (c > 1)
				notEmpty.signal();
		} finally {
			takeLock.unlock();
		}
		if (c == capacity)
			signalNotFull();
		return x;
	}

	public E poll() {
		final AtomicInteger count = this.count;
		if (count.get() == 0)
			return null;
		E x = null;
		int c = -1;
		final ReentrantLock takeLock = this.takeLock;
		takeLock.lock();
		try {
			if (count.get() > 0) {
				x = dequeue();
				c = count.getAndDecrement();
				if (c > 1)
					notEmpty.signal();
			}
		} finally {
			takeLock.unlock();
		}
		if (c == capacity)
			signalNotFull();
		return x;
	}

	public E peek() {
		if (count.get() == 0)
			return null;
		final ReentrantLock takeLock = this.takeLock;
		takeLock.lock();
		try {
			Node<E> first = head.next;
			if (first == null)
				return null;
			else
				return first.item;
		} finally {
			takeLock.unlock();
		}
	}

	/**
	 * Unlinks interior Node p with predecessor trail.
	 */
	void unlink(Node<E> p, Node<E> trail) {
		// assert isFullyLocked();
		// p.next is not changed, to allow iterators that are
		// traversing p to maintain their weak-consistency guarantee.
		p.item = null;
		trail.next = p.next;
		if (last == p)
			last = trail;
		if (count.getAndDecrement() == capacity)
			notFull.signal();
	}

	/**
	 * Removes a single instance of the specified element from this queue,
	 * if it is present.  More formally, removes an element {@code e} such
	 * that {@code o.equals(e)}, if this queue contains one or more such
	 * elements.
	 * Returns {@code true} if this queue contained the specified element
	 * (or equivalently, if this queue changed as a result of the call).
	 *
	 * @param o element to be removed from this queue, if present
	 * @return {@code true} if this queue changed as a result of the call
	 */
	public boolean remove(Object o) {
		if (o == null) return false;
		fullyLock();
		try {
			for (Node<E> trail = head, p = trail.next;
				 p != null;
				 trail = p, p = p.next) {
				if (o.equals(p.item)) {
					unlink(p, trail);
					return true;
				}
			}
			return false;
		} finally {
			fullyUnlock();
		}
	}

	/**
	 * Returns {@code true} if this queue contains the specified element.
	 * More formally, returns {@code true} if and only if this queue contains
	 * at least one element {@code e} such that {@code o.equals(e)}.
	 *
	 * @param o object to be checked for containment in this queue
	 * @return {@code true} if this queue contains the specified element
	 */
	public boolean contains(Object o) {
		if (o == null) return false;
		fullyLock();
		try {
			for (Node<E> p = head.next; p != null; p = p.next)
				if (o.equals(p.item))
					return true;
			return false;
		} finally {
			fullyUnlock();
		}
	}

	/**
	 * Returns an array containing all of the elements in this queue, in
	 * proper sequence.
	 *
	 * <p>The returned array will be "safe" in that no references to it are
	 * maintained by this queue.  (In other words, this method must allocate
	 * a new array).  The caller is thus free to modify the returned array.
	 *
	 * <p>This method acts as bridge between array-based and collection-based
	 * APIs.
	 *
	 * @return an array containing all of the elements in this queue
	 */
	public Object[] toArray() {
		fullyLock();
		try {
			int size = count.get();
			Object[] a = new Object[size];
			int k = 0;
			for (Node<E> p = head.next; p != null; p = p.next)
				a[k++] = p.item;
			return a;
		} finally {
			fullyUnlock();
		}
	}

	/**
	 * Returns an array containing all of the elements in this queue, in
	 * proper sequence; the runtime type of the returned array is that of
	 * the specified array.  If the queue fits in the specified array, it
	 * is returned therein.  Otherwise, a new array is allocated with the
	 * runtime type of the specified array and the size of this queue.
	 *
	 * <p>If this queue fits in the specified array with room to spare
	 * (i.e., the array has more elements than this queue), the element in
	 * the array immediately following the end of the queue is set to
	 * {@code null}.
	 *
	 * <p>Like the {@link #toArray()} method, this method acts as bridge between
	 * array-based and collection-based APIs.  Further, this method allows
	 * precise control over the runtime type of the output array, and may,
	 * under certain circumstances, be used to save allocation costs.
	 *
	 * <p>Suppose {@code x} is a queue known to contain only strings.
	 * The following code can be used to dump the queue into a newly
	 * allocated array of {@code String}:
	 *
	 *  <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
	 *
	 * Note that {@code toArray(new Object[0])} is identical in function to
	 * {@code toArray()}.
	 *
	 * @param a the array into which the elements of the queue are to
	 *          be stored, if it is big enough; otherwise, a new array of the
	 *          same runtime type is allocated for this purpose
	 * @return an array containing all of the elements in this queue
	 * @throws ArrayStoreException if the runtime type of the specified array
	 *         is not a supertype of the runtime type of every element in
	 *         this queue
	 * @throws NullPointerException if the specified array is null
	 */
	@SuppressWarnings("unchecked")
	public <T> T[] toArray(T[] a) {
		fullyLock();
		try {
			int size = count.get();
			if (a.length < size)
				a = (T[])java.lang.reflect.Array.newInstance
						(a.getClass().getComponentType(), size);

			int k = 0;
			for (Node<E> p = head.next; p != null; p = p.next)
				a[k++] = (T)p.item;
			if (a.length > k)
				a[k] = null;
			return a;
		} finally {
			fullyUnlock();
		}
	}

	public String toString() {
		fullyLock();
		try {
			Node<E> p = head.next;
			if (p == null)
				return "[]";

			StringBuilder sb = new StringBuilder();
			sb.append('[');
			for (;;) {
				E e = p.item;
				sb.append(e == this ? "(this Collection)" : e);
				p = p.next;
				if (p == null)
					return sb.append(']').toString();
				sb.append(',').append(' ');
			}
		} finally {
			fullyUnlock();
		}
	}

	/**
	 * Atomically removes all of the elements from this queue.
	 * The queue will be empty after this call returns.
	 */
	public void clear() {
		fullyLock();
		try {
			for (Node<E> p, h = head; (p = h.next) != null; h = p) {
				h.next = h;
				p.item = null;
			}
			head = last;
			// assert head.item == null && head.next == null;
			if (count.getAndSet(0) == capacity)
				notFull.signal();
		} finally {
			fullyUnlock();
		}
	}

	/**
	 * @throws UnsupportedOperationException {@inheritDoc}
	 * @throws ClassCastException            {@inheritDoc}
	 * @throws NullPointerException          {@inheritDoc}
	 * @throws IllegalArgumentException      {@inheritDoc}
	 */
	public int drainTo(Collection<? super E> c) {
		return drainTo(c, Integer.MAX_VALUE);
	}

	/**
	 * @throws UnsupportedOperationException {@inheritDoc}
	 * @throws ClassCastException            {@inheritDoc}
	 * @throws NullPointerException          {@inheritDoc}
	 * @throws IllegalArgumentException      {@inheritDoc}
	 */
	public int drainTo(Collection<? super E> c, int maxElements) {
		if (c == null)
			throw new NullPointerException();
		if (c == this)
			throw new IllegalArgumentException();
		if (maxElements <= 0)
			return 0;
		boolean signalNotFull = false;
		final ReentrantLock takeLock = this.takeLock;
		takeLock.lock();
		try {
			int n = Math.min(maxElements, count.get());
			// count.get provides visibility to first n Nodes
			Node<E> h = head;
			int i = 0;
			try {
				while (i < n) {
					Node<E> p = h.next;
					c.add(p.item);
					p.item = null;
					h.next = h;
					h = p;
					++i;
				}
				return n;
			} finally {
				// Restore invariants even if c.add() threw
				if (i > 0) {
					// assert h.item == null;
					head = h;
					signalNotFull = (count.getAndAdd(-i) == capacity);
				}
			}
		} finally {
			takeLock.unlock();
			if (signalNotFull)
				signalNotFull();
		}
	}

	/**
	 * Returns an iterator over the elements in this queue in proper sequence.
	 * The elements will be returned in order from first (head) to last (tail).
	 *
	 * <p>The returned iterator is
	 * <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>.
	 *
	 * @return an iterator over the elements in this queue in proper sequence
	 */
	public Iterator<E> iterator() {
		return new Itr();
	}

	private class Itr implements Iterator<E> {
		/*
		 * Basic weakly-consistent iterator.  At all times hold the next
		 * item to hand out so that if hasNext() reports true, we will
		 * still have it to return even if lost race with a take etc.
		 */

		private Node<E> current;
		private Node<E> lastRet;
		private E currentElement;

		Itr() {
			fullyLock();
			try {
				current = head.next;
				if (current != null)
					currentElement = current.item;
			} finally {
				fullyUnlock();
			}
		}

		public boolean hasNext() {
			return current != null;
		}

		/**
		 * Returns the next live successor of p, or null if no such.
		 *
		 * Unlike other traversal methods, iterators need to handle both:
		 * - dequeued nodes (p.next == p)
		 * - (possibly multiple) interior removed nodes (p.item == null)
		 */
		private Node<E> nextNode(Node<E> p) {
			for (;;) {
				Node<E> s = p.next;
				if (s == p)
					return head.next;
				if (s == null || s.item != null)
					return s;
				p = s;
			}
		}

		public E next() {
			fullyLock();
			try {
				if (current == null)
					throw new NoSuchElementException();
				E x = currentElement;
				lastRet = current;
				current = nextNode(current);
				currentElement = (current == null) ? null : current.item;
				return x;
			} finally {
				fullyUnlock();
			}
		}

		public void remove() {
			if (lastRet == null)
				throw new IllegalStateException();
			fullyLock();
			try {
				Node<E> node = lastRet;
				lastRet = null;
				for (Node<E> trail = head, p = trail.next;
					 p != null;
					 trail = p, p = p.next) {
					if (p == node) {
						unlink(p, trail);
						break;
					}
				}
			} finally {
				fullyUnlock();
			}
		}
	}

	/** A customized variant of Spliterators.IteratorSpliterator */
	static final class LBQSpliterator<E> implements Spliterator<E> {
		static final int MAX_BATCH = 1 << 25;  // max batch array size;
		final MyLinkedBlockingQueue<E> queue;
		Node<E> current;    // current node; null until initialized
		int batch;          // batch size for splits
		boolean exhausted;  // true when no more nodes
		long est;           // size estimate
		LBQSpliterator(MyLinkedBlockingQueue<E> queue) {
			this.queue = queue;
			this.est = queue.size();
		}

		public long estimateSize() { return est; }

		public Spliterator<E> trySplit() {
			Node<E> h;
			final MyLinkedBlockingQueue<E> q = this.queue;
			int b = batch;
			int n = (b <= 0) ? 1 : (b >= MAX_BATCH) ? MAX_BATCH : b + 1;
			if (!exhausted &&
					((h = current) != null || (h = q.head.next) != null) &&
					h.next != null) {
				Object[] a = new Object[n];
				int i = 0;
				Node<E> p = current;
				q.fullyLock();
				try {
					if (p != null || (p = q.head.next) != null) {
						do {
							if ((a[i] = p.item) != null)
								++i;
						} while ((p = p.next) != null && i < n);
					}
				} finally {
					q.fullyUnlock();
				}
				if ((current = p) == null) {
					est = 0L;
					exhausted = true;
				}
				else if ((est -= i) < 0L)
					est = 0L;
				if (i > 0) {
					batch = i;
					return Spliterators.spliterator
							(a, 0, i, Spliterator.ORDERED | Spliterator.NONNULL |
									Spliterator.CONCURRENT);
				}
			}
			return null;
		}

		public void forEachRemaining(Consumer<? super E> action) {
			if (action == null) throw new NullPointerException();
			final MyLinkedBlockingQueue<E> q = this.queue;
			if (!exhausted) {
				exhausted = true;
				Node<E> p = current;
				do {
					E e = null;
					q.fullyLock();
					try {
						if (p == null)
							p = q.head.next;
						while (p != null) {
							e = p.item;
							p = p.next;
							if (e != null)
								break;
						}
					} finally {
						q.fullyUnlock();
					}
					if (e != null)
						action.accept(e);
				} while (p != null);
			}
		}

		public boolean tryAdvance(Consumer<? super E> action) {
			if (action == null) throw new NullPointerException();
			final MyLinkedBlockingQueue<E> q = this.queue;
			if (!exhausted) {
				E e = null;
				q.fullyLock();
				try {
					if (current == null)
						current = q.head.next;
					while (current != null) {
						e = current.item;
						current = current.next;
						if (e != null)
							break;
					}
				} finally {
					q.fullyUnlock();
				}
				if (current == null)
					exhausted = true;
				if (e != null) {
					action.accept(e);
					return true;
				}
			}
			return false;
		}

		public int characteristics() {
			return Spliterator.ORDERED | Spliterator.NONNULL |
					Spliterator.CONCURRENT;
		}
	}

	/**
	 * Returns a {@link Spliterator} over the elements in this queue.
	 *
	 * <p>The returned spliterator is
	 * <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>.
	 *
	 * <p>The {@code Spliterator} reports {@link Spliterator#CONCURRENT},
	 * {@link Spliterator#ORDERED}, and {@link Spliterator#NONNULL}.
	 *
	 * @implNote
	 * The {@code Spliterator} implements {@code trySplit} to permit limited
	 * parallelism.
	 *
	 * @return a {@code Spliterator} over the elements in this queue
	 * @since 1.8
	 */
	public Spliterator<E> spliterator() {
		return new LBQSpliterator<E>(this);
	}

	/**
	 * Saves this queue to a stream (that is, serializes it).
	 *
	 * @param s the stream
	 * @throws java.io.IOException if an I/O error occurs
	 * @serialData The capacity is emitted (int), followed by all of
	 * its elements (each an {@code Object}) in the proper order,
	 * followed by a null
	 */
	private void writeObject(java.io.ObjectOutputStream s)
			throws java.io.IOException {

		fullyLock();
		try {
			// Write out any hidden stuff, plus capacity
			s.defaultWriteObject();

			// Write out all elements in the proper order.
			for (Node<E> p = head.next; p != null; p = p.next)
				s.writeObject(p.item);

			// Use trailing null as sentinel
			s.writeObject(null);
		} finally {
			fullyUnlock();
		}
	}

	/**
	 * Reconstitutes this queue from a stream (that is, deserializes it).
	 * @param s the stream
	 * @throws ClassNotFoundException if the class of a serialized object
	 *         could not be found
	 * @throws java.io.IOException if an I/O error occurs
	 */
	private void readObject(java.io.ObjectInputStream s)
			throws java.io.IOException, ClassNotFoundException {
		// Read in capacity, and any hidden stuff
		s.defaultReadObject();

		count.set(0);
		last = head = new Node<E>(null);

		// Read in all elements and place in queue
		for (;;) {
			@SuppressWarnings("unchecked")
			E item = (E)s.readObject();
			if (item == null){
				break;
			}
			add(item);
		}
	}
}

